How to have dynamic height in CustomMultiChildLayout?

Question

I created a CustomMultiChildLayout in order to customize the positions of its children. Then tried to put CustomMultiChildLayout into a Container, with BoxConstraints(maxHeight: 500), then the CustomMultiChildLayout has always the maxHeight 500 as height. It cannot adjust its height according to its children.

So how can I have dynamic height for my CustomMultiChildLayout? If this is not possible, are there any other ways to implement this layout?

Background:

I defined 3 widgets, each of them is a Container, and I need to customize their positions.

SellerWidget should be positioned in the middle of two other widgets.

Please refer to this image:

Here's my code:

class ProductComboWidget extends StatelessWidget {

    final Product _product;

    ProductComboWidget(this._product);

    @override
    Widget build(BuildContext context) {
        return Container(
            constraints: BoxConstraints(maxHeight: 500),
            child: CustomMultiChildLayout(
                delegate: _TitleInfoLayout(),
                children: <Widget>[
                    LayoutId(
                        id: _TitleInfoLayout.title,
                        child: ProductTitleWidget(_product)
                    ),
                    LayoutId(
                        id: _TitleInfoLayout.info,
                        child: ProductInfoWidget(_product)
                    ),
                    LayoutId(
                        id: _TitleInfoLayout.seller,
                        child: SellerWidget(_product.seller)
                    ),
                ],
            ),
        );
    }

}

class _TitleInfoLayout extends MultiChildLayoutDelegate {

    static const String title = 'title';
    static const String info = 'info';
    static const String seller = 'seller';

    @override
    void performLayout(Size size) {
        final Size titleSize = layoutChild(title, BoxConstraints(maxWidth: size.width));
        positionChild(title, Offset(0, 0));

        layoutChild(info, BoxConstraints(maxWidth: size.width));
        positionChild(info, Offset(0, titleSize.height));

        final Size sellerSize = layoutChild(seller, BoxConstraints());
        positionChild(seller, Offset(size.width - sellerSize.width - 20, titleSize.height - sellerSize.height / 2));
    }

    @override
    bool shouldRelayout(MultiChildLayoutDelegate oldDelegate) {
        return true;
    }

}

Actual result:

The height of CustomMultiChildLayout always equals to BoxConstraint.maxHeight, it cannot adjust its height according to its children.

Please refer to this image:

There is a useless empty space on the bottom of this widget.

Expected result:

Have its height adapted to its children, like other widgets.

Answer 1

Inspired by the implementation of Column and Stack, I created a custom layout to do this job. https://gist.github.com/jxw1102/a9b58a78a80c8e2f54233b418429fa50